linux/lib/sbitmap.c
David Jeffery 106397376c sbitmap: fix batching wakeup
Current code supposes that it is enough to provide forward progress by
just waking up one wait queue after one completion batch is done.

Unfortunately this way isn't enough, cause waiter can be added to wait
queue just after it is woken up.

Follows one example(64 depth, wake_batch is 8)

1) all 64 tags are active

2) in each wait queue, there is only one single waiter

3) each time one completion batch(8 completions) wakes up just one
   waiter in each wait queue, then immediately one new sleeper is added
   to this wait queue

4) after 64 completions, 8 waiters are wakeup, and there are still 8
   waiters in each wait queue

5) after another 8 active tags are completed, only one waiter can be
   wakeup, and the other 7 can't be waken up anymore.

Turns out it isn't easy to fix this problem, so simply wakeup enough
waiters for single batch.

Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Chengming Zhou <zhouchengming@bytedance.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: David Jeffery <djeffery@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/r/20230721095715.232728-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2023-07-21 11:40:20 -06:00

770 lines
18 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2016 Facebook
* Copyright (C) 2013-2014 Jens Axboe
*/
#include <linux/sched.h>
#include <linux/random.h>
#include <linux/sbitmap.h>
#include <linux/seq_file.h>
static int init_alloc_hint(struct sbitmap *sb, gfp_t flags)
{
unsigned depth = sb->depth;
sb->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
if (!sb->alloc_hint)
return -ENOMEM;
if (depth && !sb->round_robin) {
int i;
for_each_possible_cpu(i)
*per_cpu_ptr(sb->alloc_hint, i) = get_random_u32_below(depth);
}
return 0;
}
static inline unsigned update_alloc_hint_before_get(struct sbitmap *sb,
unsigned int depth)
{
unsigned hint;
hint = this_cpu_read(*sb->alloc_hint);
if (unlikely(hint >= depth)) {
hint = depth ? get_random_u32_below(depth) : 0;
this_cpu_write(*sb->alloc_hint, hint);
}
return hint;
}
static inline void update_alloc_hint_after_get(struct sbitmap *sb,
unsigned int depth,
unsigned int hint,
unsigned int nr)
{
if (nr == -1) {
/* If the map is full, a hint won't do us much good. */
this_cpu_write(*sb->alloc_hint, 0);
} else if (nr == hint || unlikely(sb->round_robin)) {
/* Only update the hint if we used it. */
hint = nr + 1;
if (hint >= depth - 1)
hint = 0;
this_cpu_write(*sb->alloc_hint, hint);
}
}
/*
* See if we have deferred clears that we can batch move
*/
static inline bool sbitmap_deferred_clear(struct sbitmap_word *map)
{
unsigned long mask;
if (!READ_ONCE(map->cleared))
return false;
/*
* First get a stable cleared mask, setting the old mask to 0.
*/
mask = xchg(&map->cleared, 0);
/*
* Now clear the masked bits in our free word
*/
atomic_long_andnot(mask, (atomic_long_t *)&map->word);
BUILD_BUG_ON(sizeof(atomic_long_t) != sizeof(map->word));
return true;
}
int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
gfp_t flags, int node, bool round_robin,
bool alloc_hint)
{
unsigned int bits_per_word;
if (shift < 0)
shift = sbitmap_calculate_shift(depth);
bits_per_word = 1U << shift;
if (bits_per_word > BITS_PER_LONG)
return -EINVAL;
sb->shift = shift;
sb->depth = depth;
sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
sb->round_robin = round_robin;
if (depth == 0) {
sb->map = NULL;
return 0;
}
if (alloc_hint) {
if (init_alloc_hint(sb, flags))
return -ENOMEM;
} else {
sb->alloc_hint = NULL;
}
sb->map = kvzalloc_node(sb->map_nr * sizeof(*sb->map), flags, node);
if (!sb->map) {
free_percpu(sb->alloc_hint);
return -ENOMEM;
}
return 0;
}
EXPORT_SYMBOL_GPL(sbitmap_init_node);
void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
{
unsigned int bits_per_word = 1U << sb->shift;
unsigned int i;
for (i = 0; i < sb->map_nr; i++)
sbitmap_deferred_clear(&sb->map[i]);
sb->depth = depth;
sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
}
EXPORT_SYMBOL_GPL(sbitmap_resize);
static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
unsigned int hint, bool wrap)
{
int nr;
/* don't wrap if starting from 0 */
wrap = wrap && hint;
while (1) {
nr = find_next_zero_bit(word, depth, hint);
if (unlikely(nr >= depth)) {
/*
* We started with an offset, and we didn't reset the
* offset to 0 in a failure case, so start from 0 to
* exhaust the map.
*/
if (hint && wrap) {
hint = 0;
continue;
}
return -1;
}
if (!test_and_set_bit_lock(nr, word))
break;
hint = nr + 1;
if (hint >= depth - 1)
hint = 0;
}
return nr;
}
static int sbitmap_find_bit_in_word(struct sbitmap_word *map,
unsigned int depth,
unsigned int alloc_hint,
bool wrap)
{
int nr;
do {
nr = __sbitmap_get_word(&map->word, depth,
alloc_hint, wrap);
if (nr != -1)
break;
if (!sbitmap_deferred_clear(map))
break;
} while (1);
return nr;
}
static int sbitmap_find_bit(struct sbitmap *sb,
unsigned int depth,
unsigned int index,
unsigned int alloc_hint,
bool wrap)
{
unsigned int i;
int nr = -1;
for (i = 0; i < sb->map_nr; i++) {
nr = sbitmap_find_bit_in_word(&sb->map[index],
min_t(unsigned int,
__map_depth(sb, index),
depth),
alloc_hint, wrap);
if (nr != -1) {
nr += index << sb->shift;
break;
}
/* Jump to next index. */
alloc_hint = 0;
if (++index >= sb->map_nr)
index = 0;
}
return nr;
}
static int __sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint)
{
unsigned int index;
index = SB_NR_TO_INDEX(sb, alloc_hint);
/*
* Unless we're doing round robin tag allocation, just use the
* alloc_hint to find the right word index. No point in looping
* twice in find_next_zero_bit() for that case.
*/
if (sb->round_robin)
alloc_hint = SB_NR_TO_BIT(sb, alloc_hint);
else
alloc_hint = 0;
return sbitmap_find_bit(sb, UINT_MAX, index, alloc_hint,
!sb->round_robin);
}
int sbitmap_get(struct sbitmap *sb)
{
int nr;
unsigned int hint, depth;
if (WARN_ON_ONCE(unlikely(!sb->alloc_hint)))
return -1;
depth = READ_ONCE(sb->depth);
hint = update_alloc_hint_before_get(sb, depth);
nr = __sbitmap_get(sb, hint);
update_alloc_hint_after_get(sb, depth, hint, nr);
return nr;
}
EXPORT_SYMBOL_GPL(sbitmap_get);
static int __sbitmap_get_shallow(struct sbitmap *sb,
unsigned int alloc_hint,
unsigned long shallow_depth)
{
unsigned int index;
index = SB_NR_TO_INDEX(sb, alloc_hint);
alloc_hint = SB_NR_TO_BIT(sb, alloc_hint);
return sbitmap_find_bit(sb, shallow_depth, index, alloc_hint, true);
}
int sbitmap_get_shallow(struct sbitmap *sb, unsigned long shallow_depth)
{
int nr;
unsigned int hint, depth;
if (WARN_ON_ONCE(unlikely(!sb->alloc_hint)))
return -1;
depth = READ_ONCE(sb->depth);
hint = update_alloc_hint_before_get(sb, depth);
nr = __sbitmap_get_shallow(sb, hint, shallow_depth);
update_alloc_hint_after_get(sb, depth, hint, nr);
return nr;
}
EXPORT_SYMBOL_GPL(sbitmap_get_shallow);
bool sbitmap_any_bit_set(const struct sbitmap *sb)
{
unsigned int i;
for (i = 0; i < sb->map_nr; i++) {
if (sb->map[i].word & ~sb->map[i].cleared)
return true;
}
return false;
}
EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);
static unsigned int __sbitmap_weight(const struct sbitmap *sb, bool set)
{
unsigned int i, weight = 0;
for (i = 0; i < sb->map_nr; i++) {
const struct sbitmap_word *word = &sb->map[i];
unsigned int word_depth = __map_depth(sb, i);
if (set)
weight += bitmap_weight(&word->word, word_depth);
else
weight += bitmap_weight(&word->cleared, word_depth);
}
return weight;
}
static unsigned int sbitmap_cleared(const struct sbitmap *sb)
{
return __sbitmap_weight(sb, false);
}
unsigned int sbitmap_weight(const struct sbitmap *sb)
{
return __sbitmap_weight(sb, true) - sbitmap_cleared(sb);
}
EXPORT_SYMBOL_GPL(sbitmap_weight);
void sbitmap_show(struct sbitmap *sb, struct seq_file *m)
{
seq_printf(m, "depth=%u\n", sb->depth);
seq_printf(m, "busy=%u\n", sbitmap_weight(sb));
seq_printf(m, "cleared=%u\n", sbitmap_cleared(sb));
seq_printf(m, "bits_per_word=%u\n", 1U << sb->shift);
seq_printf(m, "map_nr=%u\n", sb->map_nr);
}
EXPORT_SYMBOL_GPL(sbitmap_show);
static inline void emit_byte(struct seq_file *m, unsigned int offset, u8 byte)
{
if ((offset & 0xf) == 0) {
if (offset != 0)
seq_putc(m, '\n');
seq_printf(m, "%08x:", offset);
}
if ((offset & 0x1) == 0)
seq_putc(m, ' ');
seq_printf(m, "%02x", byte);
}
void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
{
u8 byte = 0;
unsigned int byte_bits = 0;
unsigned int offset = 0;
int i;
for (i = 0; i < sb->map_nr; i++) {
unsigned long word = READ_ONCE(sb->map[i].word);
unsigned long cleared = READ_ONCE(sb->map[i].cleared);
unsigned int word_bits = __map_depth(sb, i);
word &= ~cleared;
while (word_bits > 0) {
unsigned int bits = min(8 - byte_bits, word_bits);
byte |= (word & (BIT(bits) - 1)) << byte_bits;
byte_bits += bits;
if (byte_bits == 8) {
emit_byte(m, offset, byte);
byte = 0;
byte_bits = 0;
offset++;
}
word >>= bits;
word_bits -= bits;
}
}
if (byte_bits) {
emit_byte(m, offset, byte);
offset++;
}
if (offset)
seq_putc(m, '\n');
}
EXPORT_SYMBOL_GPL(sbitmap_bitmap_show);
static unsigned int sbq_calc_wake_batch(struct sbitmap_queue *sbq,
unsigned int depth)
{
unsigned int wake_batch;
unsigned int shallow_depth;
/*
* For each batch, we wake up one queue. We need to make sure that our
* batch size is small enough that the full depth of the bitmap,
* potentially limited by a shallow depth, is enough to wake up all of
* the queues.
*
* Each full word of the bitmap has bits_per_word bits, and there might
* be a partial word. There are depth / bits_per_word full words and
* depth % bits_per_word bits left over. In bitwise arithmetic:
*
* bits_per_word = 1 << shift
* depth / bits_per_word = depth >> shift
* depth % bits_per_word = depth & ((1 << shift) - 1)
*
* Each word can be limited to sbq->min_shallow_depth bits.
*/
shallow_depth = min(1U << sbq->sb.shift, sbq->min_shallow_depth);
depth = ((depth >> sbq->sb.shift) * shallow_depth +
min(depth & ((1U << sbq->sb.shift) - 1), shallow_depth));
wake_batch = clamp_t(unsigned int, depth / SBQ_WAIT_QUEUES, 1,
SBQ_WAKE_BATCH);
return wake_batch;
}
int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
int shift, bool round_robin, gfp_t flags, int node)
{
int ret;
int i;
ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node,
round_robin, true);
if (ret)
return ret;
sbq->min_shallow_depth = UINT_MAX;
sbq->wake_batch = sbq_calc_wake_batch(sbq, depth);
atomic_set(&sbq->wake_index, 0);
atomic_set(&sbq->ws_active, 0);
atomic_set(&sbq->completion_cnt, 0);
atomic_set(&sbq->wakeup_cnt, 0);
sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
if (!sbq->ws) {
sbitmap_free(&sbq->sb);
return -ENOMEM;
}
for (i = 0; i < SBQ_WAIT_QUEUES; i++)
init_waitqueue_head(&sbq->ws[i].wait);
return 0;
}
EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
unsigned int depth)
{
unsigned int wake_batch;
wake_batch = sbq_calc_wake_batch(sbq, depth);
if (sbq->wake_batch != wake_batch)
WRITE_ONCE(sbq->wake_batch, wake_batch);
}
void sbitmap_queue_recalculate_wake_batch(struct sbitmap_queue *sbq,
unsigned int users)
{
unsigned int wake_batch;
unsigned int depth = (sbq->sb.depth + users - 1) / users;
wake_batch = clamp_val(depth / SBQ_WAIT_QUEUES,
1, SBQ_WAKE_BATCH);
WRITE_ONCE(sbq->wake_batch, wake_batch);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_recalculate_wake_batch);
void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
{
sbitmap_queue_update_wake_batch(sbq, depth);
sbitmap_resize(&sbq->sb, depth);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
int __sbitmap_queue_get(struct sbitmap_queue *sbq)
{
return sbitmap_get(&sbq->sb);
}
EXPORT_SYMBOL_GPL(__sbitmap_queue_get);
unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
unsigned int *offset)
{
struct sbitmap *sb = &sbq->sb;
unsigned int hint, depth;
unsigned long index, nr;
int i;
if (unlikely(sb->round_robin))
return 0;
depth = READ_ONCE(sb->depth);
hint = update_alloc_hint_before_get(sb, depth);
index = SB_NR_TO_INDEX(sb, hint);
for (i = 0; i < sb->map_nr; i++) {
struct sbitmap_word *map = &sb->map[index];
unsigned long get_mask;
unsigned int map_depth = __map_depth(sb, index);
sbitmap_deferred_clear(map);
if (map->word == (1UL << (map_depth - 1)) - 1)
goto next;
nr = find_first_zero_bit(&map->word, map_depth);
if (nr + nr_tags <= map_depth) {
atomic_long_t *ptr = (atomic_long_t *) &map->word;
unsigned long val;
get_mask = ((1UL << nr_tags) - 1) << nr;
val = READ_ONCE(map->word);
while (!atomic_long_try_cmpxchg(ptr, &val,
get_mask | val))
;
get_mask = (get_mask & ~val) >> nr;
if (get_mask) {
*offset = nr + (index << sb->shift);
update_alloc_hint_after_get(sb, depth, hint,
*offset + nr_tags - 1);
return get_mask;
}
}
next:
/* Jump to next index. */
if (++index >= sb->map_nr)
index = 0;
}
return 0;
}
int sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
unsigned int shallow_depth)
{
WARN_ON_ONCE(shallow_depth < sbq->min_shallow_depth);
return sbitmap_get_shallow(&sbq->sb, shallow_depth);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_get_shallow);
void sbitmap_queue_min_shallow_depth(struct sbitmap_queue *sbq,
unsigned int min_shallow_depth)
{
sbq->min_shallow_depth = min_shallow_depth;
sbitmap_queue_update_wake_batch(sbq, sbq->sb.depth);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_min_shallow_depth);
static void __sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr)
{
int i, wake_index, woken;
if (!atomic_read(&sbq->ws_active))
return;
wake_index = atomic_read(&sbq->wake_index);
for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
struct sbq_wait_state *ws = &sbq->ws[wake_index];
/*
* Advance the index before checking the current queue.
* It improves fairness, by ensuring the queue doesn't
* need to be fully emptied before trying to wake up
* from the next one.
*/
wake_index = sbq_index_inc(wake_index);
if (waitqueue_active(&ws->wait)) {
woken = wake_up_nr(&ws->wait, nr);
if (woken == nr)
break;
nr -= woken;
}
}
if (wake_index != atomic_read(&sbq->wake_index))
atomic_set(&sbq->wake_index, wake_index);
}
void sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr)
{
unsigned int wake_batch = READ_ONCE(sbq->wake_batch);
unsigned int wakeups;
if (!atomic_read(&sbq->ws_active))
return;
atomic_add(nr, &sbq->completion_cnt);
wakeups = atomic_read(&sbq->wakeup_cnt);
do {
if (atomic_read(&sbq->completion_cnt) - wakeups < wake_batch)
return;
} while (!atomic_try_cmpxchg(&sbq->wakeup_cnt,
&wakeups, wakeups + wake_batch));
__sbitmap_queue_wake_up(sbq, wake_batch);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
static inline void sbitmap_update_cpu_hint(struct sbitmap *sb, int cpu, int tag)
{
if (likely(!sb->round_robin && tag < sb->depth))
data_race(*per_cpu_ptr(sb->alloc_hint, cpu) = tag);
}
void sbitmap_queue_clear_batch(struct sbitmap_queue *sbq, int offset,
int *tags, int nr_tags)
{
struct sbitmap *sb = &sbq->sb;
unsigned long *addr = NULL;
unsigned long mask = 0;
int i;
smp_mb__before_atomic();
for (i = 0; i < nr_tags; i++) {
const int tag = tags[i] - offset;
unsigned long *this_addr;
/* since we're clearing a batch, skip the deferred map */
this_addr = &sb->map[SB_NR_TO_INDEX(sb, tag)].word;
if (!addr) {
addr = this_addr;
} else if (addr != this_addr) {
atomic_long_andnot(mask, (atomic_long_t *) addr);
mask = 0;
addr = this_addr;
}
mask |= (1UL << SB_NR_TO_BIT(sb, tag));
}
if (mask)
atomic_long_andnot(mask, (atomic_long_t *) addr);
smp_mb__after_atomic();
sbitmap_queue_wake_up(sbq, nr_tags);
sbitmap_update_cpu_hint(&sbq->sb, raw_smp_processor_id(),
tags[nr_tags - 1] - offset);
}
void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
unsigned int cpu)
{
/*
* Once the clear bit is set, the bit may be allocated out.
*
* Orders READ/WRITE on the associated instance(such as request
* of blk_mq) by this bit for avoiding race with re-allocation,
* and its pair is the memory barrier implied in __sbitmap_get_word.
*
* One invariant is that the clear bit has to be zero when the bit
* is in use.
*/
smp_mb__before_atomic();
sbitmap_deferred_clear_bit(&sbq->sb, nr);
/*
* Pairs with the memory barrier in set_current_state() to ensure the
* proper ordering of clear_bit_unlock()/waitqueue_active() in the waker
* and test_and_set_bit_lock()/prepare_to_wait()/finish_wait() in the
* waiter. See the comment on waitqueue_active().
*/
smp_mb__after_atomic();
sbitmap_queue_wake_up(sbq, 1);
sbitmap_update_cpu_hint(&sbq->sb, cpu, nr);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_clear);
void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
{
int i, wake_index;
/*
* Pairs with the memory barrier in set_current_state() like in
* sbitmap_queue_wake_up().
*/
smp_mb();
wake_index = atomic_read(&sbq->wake_index);
for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
struct sbq_wait_state *ws = &sbq->ws[wake_index];
if (waitqueue_active(&ws->wait))
wake_up(&ws->wait);
wake_index = sbq_index_inc(wake_index);
}
}
EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);
void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
{
bool first;
int i;
sbitmap_show(&sbq->sb, m);
seq_puts(m, "alloc_hint={");
first = true;
for_each_possible_cpu(i) {
if (!first)
seq_puts(m, ", ");
first = false;
seq_printf(m, "%u", *per_cpu_ptr(sbq->sb.alloc_hint, i));
}
seq_puts(m, "}\n");
seq_printf(m, "wake_batch=%u\n", sbq->wake_batch);
seq_printf(m, "wake_index=%d\n", atomic_read(&sbq->wake_index));
seq_printf(m, "ws_active=%d\n", atomic_read(&sbq->ws_active));
seq_puts(m, "ws={\n");
for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
struct sbq_wait_state *ws = &sbq->ws[i];
seq_printf(m, "\t{.wait=%s},\n",
waitqueue_active(&ws->wait) ? "active" : "inactive");
}
seq_puts(m, "}\n");
seq_printf(m, "round_robin=%d\n", sbq->sb.round_robin);
seq_printf(m, "min_shallow_depth=%u\n", sbq->min_shallow_depth);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_show);
void sbitmap_add_wait_queue(struct sbitmap_queue *sbq,
struct sbq_wait_state *ws,
struct sbq_wait *sbq_wait)
{
if (!sbq_wait->sbq) {
sbq_wait->sbq = sbq;
atomic_inc(&sbq->ws_active);
add_wait_queue(&ws->wait, &sbq_wait->wait);
}
}
EXPORT_SYMBOL_GPL(sbitmap_add_wait_queue);
void sbitmap_del_wait_queue(struct sbq_wait *sbq_wait)
{
list_del_init(&sbq_wait->wait.entry);
if (sbq_wait->sbq) {
atomic_dec(&sbq_wait->sbq->ws_active);
sbq_wait->sbq = NULL;
}
}
EXPORT_SYMBOL_GPL(sbitmap_del_wait_queue);
void sbitmap_prepare_to_wait(struct sbitmap_queue *sbq,
struct sbq_wait_state *ws,
struct sbq_wait *sbq_wait, int state)
{
if (!sbq_wait->sbq) {
atomic_inc(&sbq->ws_active);
sbq_wait->sbq = sbq;
}
prepare_to_wait_exclusive(&ws->wait, &sbq_wait->wait, state);
}
EXPORT_SYMBOL_GPL(sbitmap_prepare_to_wait);
void sbitmap_finish_wait(struct sbitmap_queue *sbq, struct sbq_wait_state *ws,
struct sbq_wait *sbq_wait)
{
finish_wait(&ws->wait, &sbq_wait->wait);
if (sbq_wait->sbq) {
atomic_dec(&sbq->ws_active);
sbq_wait->sbq = NULL;
}
}
EXPORT_SYMBOL_GPL(sbitmap_finish_wait);